inserting in binary tree doesn't work using java

问题

I'm currently learning about trees using java and i have some errors going on here in the insertion of items in a binary tree I don't why it doesn't work

this is the code: tree node:

public class TNode {
    int data;
    TNode left;
    TNode right;

    public TNode(int data) {
        this.data = data;
        left = null;
        right = null;
    }
}

tree class:

public class Tree {
    TNode root;

    public Tree(){
        root = null;
    }

    public TNode insertNode(TNode item, int d) {
        if (item == null) {
            return new TNode(d);
        }

         if (d < item.data) {
            item.left = insertNode(item, d);
        }

        if (d > item.data) {
            item.right = insertNode(item, d);
        } else {
            return item;
        }

        return item;
    }

    public void add(int d) {
        insertNode(root, d);
    }
}

Whenever I add an item the root remains null with no right or left items if someone can help I'll be really thankful

回答1:

root is always null because you never assign value to it.

you can add to the beginning of your method check and assign it

public TNode insertNode(TNode item, int d){
    if(item == null){
        TNode node = new TNode(d);
        if (root == null) { 
            root = node;
        }
        return node
    }
    ... rest of method isn't changed...

Also when you are recursing you should make a call with a proper child node instead of always calling with item, so for example first case would be:

    item.left = insertNode(item.left, d);

For second case you would just use item.right instead.

回答2:

Fine code, but recursing does not step further

item.left = insertNode(item.left, d);
item.right = insertNode(item.right, d);

And the initial root is not updated:

root = insertNode(root, d);

The else part or final return is superfluous.

Something on the code style

insertNode has a node as input, and returns the updated node value, hence the call "pattern" should look like

X = insertNode(X, d); // X is some expression

This is because java can never assign to the passed argument expression: it has no pass-by-reference, but pass-by-value; f(x) never assigns to x.

来源：https://stackoverflow.com/questions/50193957/inserting-in-binary-tree-doesnt-work-using-java

标签

java

data-structures

tree

binary